Output voltage detection circuit for traffic signal controller

ABSTRACT

An improved output voltage detection circuit for a traffic signal controller which is capable of minimizing an operational characteristic variation with respect to the operational temperature variation and enabling a compact product. The circuit includes a detection voltage dividing unit for dividing a detection input voltage having an alternating current component applied to a traffic signal system into voltages having a predetermined level, a latch unit for latching a voltage from the detection voltage dividing unit and generating a detection output voltage, a zero crossing detection signal generation unit for detecting a zero crossing timing from an alternating current voltage power and generating a zero crossing detection signal, a memory unit for storing a delay algorithm therein, and a central processing unit (CPU) for reading a delay algorithm the zero crossing detection signal from the memory unit, performing a delay programming, and applying a latch clock signal to the latch unit as much as a programmed delay constant.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an output voltage detection circuit fora traffic signal controller, and in particular to an improved outputvoltage detection circuit for a traffic signal controller which iscapable of reducing a characteristic variation based on an operationaltemperature variation, implementing a hybrid integration device,enabling a compact product, and adjusting a detection reference point bya software-based method.

2. Description of the Conventional Art

In the traffic signal controller, there is provided a function that thestate of a traffic light ON/OFF signal (lamp on/off signal) is detectedin real time for evaluating whether a signal control is normallyperformed.

The method for detecting whether a signal control is normally performedis classified into two methods. Between the methods, a method isdirected to detecting whether a voltage is normally supplied to atraffic light ON/OFF cable which outputs an ON signal, and the othermethod is directed to detecting whether a voltage is not supplied to atraffic light ON/OFF cable which outputs an OFF signal.

Generally, since checking whether an ON state is correctly generated isimportant, among the above-described detection methods, the previousmethod is used for the group of red lights (PR: a pedestrian red light,R: a vehicle red light, Y: a vehicle yellow light). In addition, sincewhether an OFF state is correctly generated is important, among theabove-described detection methods, the later method is used for thegroup of green light (PG: a pedestrian green light, G: a vehicle greenlight, A: a vehicle left-turn or right-turn light.

In the traffic signal controller, to detect whether a voltage isnormally inputted into the traffic signal controller is important. Inthe normal state, a traffic signal control is continuously performed. Inthe abnormal state, a traffic signal control is stopped because atraffic accident may occur, and an on-and-off operation is performed.

As shown in FIG. 1, the conventional output voltage detection circuitfor a traffic signal controller includes a detection voltage dividingunit 11 for dividing a detection input voltage VI having an alternatingcurrent component, which is applied to a traffic signal system, intovoltages having a predetermined level, a photo-coupler 12 for receivingan output voltage from the detection voltage dividing unit 11, and asignal converter 13 for outputting a low level voltage when a voltage isperiodically inputted through the photo-coupler 12 and outputting a highlevel voltage when a voltage is periodically not inputted.

Here, the detection voltage dividing unit 11 includes a resistor R11which is connected in series with the input terminal, and a diode D11and a resistor R12 which are connected in parallel with the resistor R11and the input terminal.

The photo-coupler 12 includes a light emitting diode LED connected inparallel with the detection voltage dividing unit 11 and the resistorR12, and a photo-transistor PTR which is turned on and off in accordancewith a detection of the light emitting diode LED.

In addition, the signal converter 13 includes a resistor R13 connectedbetween a power terminal voltage VCC and a photo-transistor PTR of thephoto-coupler 12, a resistor R14 and a condenser C11 connected in seriesbetween the collector of he photo-transistor PTR of the photo-coupler 12and a ground, a diode D12 connected in parallel with the resistor R14,and an output buffer BUF11 commonly connected with the resistor R14 andthe condenser C11 for outputting an output detection voltage VO.

The operation of the conventional output voltage detection circuit for atraffic signal controller will now be explained with reference to theaccompanying drawings.

First, when a power is supplied to a traffic signal ON/OFF cable forturning on/off the traffic signals, the detection input voltage VIhaving an alternating current component which is fed-back from thetraffic signal ON/OFF cable is divided into voltages having apredetermined level by the resistors R11 and R12 and the thusly dividedvoltages are supplied to the photo-coupler 12.

Here, when the detection input voltage VI is normally inputted, thelevel thereof is ranged from 120 volts to 220 volts. The light emittingdiode LED and the photo-transistor PTR of the photo-coupler 12 arerepeatedly turned on/off at a period corresponding to the powerfrequency.

Namely, when the detection input voltage VI is inputted, thephoto-transistor PTR of the photo-coupler 12 is turned on, and the powerterminal voltage VCC is applied to the ground terminal through thephoto-transistor PTR. A waveform as shown in FIG. 2B is outputted in theinterval T1 from the collector of the photo-transistor PTR. When thedetection input voltage VI is not applied, since the photo-transistorPTR of the photo-coupler 12 is turned off, and the power terminalvoltage VCC is charged by a time constant (T=R14×C11) into the condenserC11 through the resistor R14, the collector of the photo-transistor PTRoutputs a high level voltage in the interval T2 as shown in FIG. 2B.

At this time, at the moment when the photo-transistor PTR is turned on,since the voltage is quickly discharged from the diode D12 and thephoto-transistor PTR of the signal converter 13 to a ground, while thepower is supplied to the traffic signal on/off cable, namely, while thedetection input voltage VI is inputted, the output buffer BUF11 outputsa low level detection output voltage VO in the interval T1 as shown inFIG. 2.

On the contrary, when a detection input voltage VI is not inputted, ahigh level detection output voltage VO as shown in FIG. 2C is outputtedin the interval T2.

The detection output voltage VO outputted from the output buffer BUF11of the signal converter 13 is applied to the system controller (notshown). The system controller (not shown) judges whether a voltageinput/output is normally performed with respect to the traffic signal.

Generally, the operational temperature of the traffic signal system isset at -34° C.˜+74° C. The voltage feeding-back system is configuredsuch that an input voltage is not detected below AC 15 volts, and theinput voltage is detected above AC 25 volts.

In addition, the traffic signal controller is configured such that 48traffic lights are driven. Therefore, the traffic signal controlleroutputs 48 has an output circuit of 48 signals. Therefore, in the outputvoltage feeding-back circuit, the routines are performed 48 time.

However, in the conventional output voltage detection circuit for atraffic signal controller, the photo-coupler 12 is installed as animportant element in the circuit. Since the turning-on current of thephoto-coupler 12 is varied, the start point of the detection voltage isdisadvantageously varied. In addition, it is difficult to configure theapparatus which is capable of satisfying the voltage detectioncharacteristic within a range of the operational temperature of theapparatus.

Furthermore, since it is difficult to manufacture a hybrid IC consistingof the photo-transistor PTR and the light emitting device (LED), it isimpossible to manufacture a compact product.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide anoutput voltage detection circuit for a traffic signal controller whichovercomes the aforementioned problem encountered in the conventionalart.

It is another object of the present invention to provide an improvedoutput voltage detection circuit for a traffic signal controller whichis capable of minimizing an operational characteristic variation withrespect to the operational temperature variation and enabling a compactproduct.

To achieve the above objects, there is provided an output voltagedetection circuit for a traffic signal controller which includes adetection voltage dividing unit for dividing a detection input voltagehaving an alternating current component applied to a traffic signalsystem into voltages having a predetermined level, a latch unit forlatching a voltage from the detection voltage dividing unit andgenerating a detection output voltage, a zero crossing detection signalgeneration unit for detecting a zero crossing timing from an alternatingcurrent voltage power and generating a zero crossing detection signal, amemory unit for storing a delay algorithm therein, and a centralprocessing unit (CPU) for reading a delay algorithm the zero crossingdetection signal from the memory unit, performing a delay programming,and applying a latch clock signal to the latch unit as much as aprogrammed delay constant.

Additional advantages, objects and features of the invention will becomemore apparent from the description which follows.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more fully understood from thedetailed description given hereinbelow and the accompanying drawingswhich are given by way of illustration only, and thus are not limitativeof the present invention, and wherein:

FIG. 1 is a circuit diagram illustrating a conventional output voltagedetection circuit for a traffic signal controller;

FIGS. 2A through 2C are waveform diagrams of signals in the circuit ofFIG. 1;

FIG. 3 is a circuit diagram illustrating an output voltage detectioncircuit for a traffic signal controller according to the presentinvention; and

FIGS. 4A through 4E are waveform diagrams of signals in the circuit ofFIG. 3.

DETAILED DESCRIPTION OF THE INVENTION

As shown in FIG. 3, the output voltage detection circuit for a trafficsignal controller according to the present invention includes adetection voltage dividing unit 31 for dividing a detection inputvoltage VI having an alternating current component which is applied to atraffic signal system into voltage having a predetermined level, a latchunit 32 for latching a voltage from the detection voltage dividing unit31 and outputting the same as a detection output voltage VO, a zerocrossing detection signal generation unit 34 for detecting a zerocrossing timing from the alternating current voltage AC and generating azero crossing detection signal ZC, a memory unit 35 for storing a delayalgorithm therein, and a central processing unit 33 for reading a delayalgorithm from the memory unit 35, performing a delay program, delayingthe same for as much as the programmed delay constant DK, and outputtinga latch clock signal LCK to the latch unit 32.

Here, the detection voltage dividing unit 31 includes a resistor R31connected between an input terminal receiving a detection input voltageVI and an input terminal D of the latch unit 32, a resistor R32connected between another input terminal receiving the detection inputvoltage VI and the input terminal D of the latch unit 32, and acondenser C31 connected in parallel with the resistor R32.

As the latch unit 32, a D-type flip-flop 32-1 is used in the presentinvention.

In addition, the central processing unit 33 includes a delay processingunit 33-3 for receiving a zero-crossing detection signal ZC from thezero crossing detection signal generation unit 34, delaying the same fora predetermined time by the delay constant DK programmed based on thedelay algorithm read from the memory unit 35, and outputting a latchclock signal LCK to the clock signal input terminal CK of the D-typeflip-flop 32-1 of the latch unit 32.

The operation of the output voltage detection circuit for a trafficsignal controller according to the present invention will now beexplained with reference to the accompanying drawings.

First, when supplying a power to the traffic light ON/OFF cable forturning on the traffic light, the detection input voltage VI having analternating current component, as shown in FIG. 4D, from the trafficlight ON/OFF cable is divided into voltages having a predetermined levelby the resistors R31 and R32 and is charged into the condenser C31. Thethusly charged voltage is applied to the input terminal D of the D-typeflip-flop 32-1 of the latch unit 32. Here, the level of the voltageapplied to the input terminal D is a TTL level of about 5 volts.

The resistance values of the resistors R31 and R32 are computed and setsuch that the D-type flip-flop 32-1 recognizes the voltage value at theinput terminal D as a high level value when the detection input voltageVI reaches a detection reference value, namely, a start voltage at whichthe presence of the voltage is recognized.

The D-type flip-flop 32-1 is a device which is capable of maintainingthe level of the input terminal D from a rising edge input timing of thelatch clock signal LCK to a rising edge input timing of the next latchclock signal LCK. Namely, the voltage supplied to the input terminal Dis latched in synchronization with the rising edge of the latch clocksignal LCK, as shown in FIG. 4C, supplied from the central processingunit 33.

Therefore, in the D-type flip-flop 32-1, the detection output voltage VOis outputted in accordance with a condition that whether a detectioninput voltage VI is inputted from the output terminal /Q insynchronization with the latch clock signal LCK.

As shown in FIG. 4A, an alternating current voltage i applied to thezero crossing detection signal generation unit 34, the zero crossingdetection signal generation unit 34 detects a zero crossing timing andgenerates a zero crossing detection signal ZC as shown in FIG. 4B. Whenthe zero crossing detection signal ZC is applied to the centralprocessing apparatus 33, the delay processing unit 33-1 of the centralprocessing unit 33 reads a delay algorithm from the memory unit 35,performs the delay program, generates a latch clock signal LCK, as shownin FIG. 4C, which is obtained by delaying the zero crossing detectionsignal ZC as much as the programmed delay constant DK, and outputs thethusly generated latch clock signal LCK to the clock signal inputterminal CK of the D-type flip-flop 32-1.

In the D-type flip-flop 32-1 of the latch unit 32, a detection outputvoltage VO, as shown in FIG. 4E, is outputted from the output terminalin synchronization with the latch clock signal LCK.

Therefore, it is possible to adjust the latch timing of the D-typeflip-flop 32-1 by using the programmed delay constant DK. Therefore,even though the detection input voltage VI is an alternating currentvoltage which is varied in accordance with a time lapse, it is possibleto latch at the peak point of the alternating current voltage inaccordance with a latching timing and to latch at a point near the peakpoint, so that it is possible to vary a predetermined detectionreference value.

As described above, since the latch clock signal LCK delayed by usingthe latch device and the delay constant DK programmed by the delayalgorithm is used as a clock signal for the D-type flip-flop 32-1 of thelatch unit 32, it is possible to accurately adjust a detecting timing.In addition, it is possible to easily implement a voltage feeding-backcircuit within an operational temperature range (generally, -34° C.˜+74°C.) of a traffic signal system by minimizing the variation of acharacteristic with respect to the operational temperature variation.Namely, when an input voltage is below AC 15 volts, the voltage is notdetected, and when the input voltage is above AC 25 volts, the voltageis detected. Furthermore, it is possible to implement all devices as ahybrid integration device, and it is possible to manufacture a compactproduct.

Although the preferred embodiments of the present invention have beendisclosed for illustrative purposes, those skilled in the art willappreciate that various modifications, additions and substitutions arepossible, without departing from the scope and spirit of the inventionas recited in the accompanying claims.

What is claimed is:
 1. An output voltage detection circuit for a trafficsignal controller, comprising:a detection voltage dividing unit fordividing a detection input voltage having an alternating currentcomponent applied to a traffic signal system into voltages having apredetermined level; latch means for latching a voltage from thedetection voltage dividing unit and generating a detection outputvoltage; zero crossing detection signal generation means for detecting azero crossing timing from an alternating current voltage power andgenerating a zero crossing detection signal; memory means for storing adelay algorithm therein; and a central processing unit for supplying alatch clock signal to the latch means wherein the latch clock signal isa delayed version of the zero crossing detection signal, the delay beinga function of the delay algorithm.
 2. The circuit of claim 1, whereinsaid central processing unit includes a delay processing means whereinthe delay processing means supplies the latch clock signal to the latchmeans wherein the latch clock signal is the delayed version of the zerocrossing detection signal, the delay being a function of the delayalgorithm.
 3. The circuit of claim 1, wherein said latch means uses thelatch clock signal from the central processing unit as a clock signalinput and includes a D-type flip-flop which is synchronized by the clocksignal input.
 4. The circuit of claim 1, wherein said detection voltagedividing unit includes:a dividing unit for dividing the detection inputvoltage which is applied to the traffic light system; and a capacitorfor charging a divided voltage therein.
 5. The circuit of claim 4,wherein said capacitor is used for protecting the output voltagedetection circuit from surges.